Mini-lag spikes every 30 seconds

I am having this problem ever since I bought my new PC and connected to my homes network which in turn is connect to 2 other computers. I am having this problem on ONLY this computer and ONLY this game.. no lag spikes in men of war L4D so on and so fourth. i tried everything in the stickied thread but i don't know what to do.It jumps up to 1,500ms every 30 seconds making really hard to monk and do kilroy brawling and would appreceiate some help.

the 2 other computer will eat bandwith, turn them off if possible. if not try to play in few hours, could be the server.

Firewall settings maybe? Or anything else running in your background?

Since this is the only computer having issues and there was none til you got a new one I'd assume it's something on your end =\